Bottom Line:
The crystal nanocavity used in this study consisted of a defective photonic crystal beam coupled to a metal surface with a nanoscale air gap in between and provided hybridization of a highly confined plasmonic-photonic mode with a high quality factor and deep subwavelength mode volume.Efficient photon-phonon interaction occurs in the air gap through the SAW perturbation of the metal surface, strongly coupling the optical and acoustic frequencies.As a result, a large modulation bandwidth and optical resonance wavelength shift for the crystal nanocavity are demonstrated at telecommunication wavelengths.

ABSTRACTWe propose dynamic modulation of a hybrid plasmonic-photonic crystal nanocavity using monochromatic coherent acoustic phonons formed by ultrahigh-frequency surface acoustic waves (SAWs) to achieve strong optomechanical interaction. The crystal nanocavity used in this study consisted of a defective photonic crystal beam coupled to a metal surface with a nanoscale air gap in between and provided hybridization of a highly confined plasmonic-photonic mode with a high quality factor and deep subwavelength mode volume. Efficient photon-phonon interaction occurs in the air gap through the SAW perturbation of the metal surface, strongly coupling the optical and acoustic frequencies. As a result, a large modulation bandwidth and optical resonance wavelength shift for the crystal nanocavity are demonstrated at telecommunication wavelengths. The proposed SAW-based modulation within the hybrid plasmonic-photonic crystal nanocavities beyond the diffraction limit provides opportunities for various applications in enhanced sound-light interaction and fast coherent acoustic control of optomechanical devices.

f3: /E/2 and /Ey/2 field distributions of the SPP cavity mode on the (a) x-y and (b) x-z planes, respectively.The result is obtained using the supercell approach with seven lattice periods on each side of the cavity. The cavity mode is confined by the cavity and squeezed inside the air gap. Variations of the /E/2 field for the cavity mode (c) at the center of the air gap along the x-direction and (d) close to the middle of the defect along the y-direction, respectively. In (c) x/a = 0 denotes the cavity center, and in (d) y/d = 0 denotes the silver substrate surface.

Mentions:
We generated defects in the structure to serve as a nanocavity by removing two circular air holes at the middle of the silicon photonic crystal beam, as shown in Figs 1a and 3a. The nanocavity supported a highly confined SPP cavity mode by means of the simultaneous SPP and bandgap effects, which confine propagation along the z-direction and x-direction, respectively. Fig. 3a,b show clearly the confinement of the field distributions /E/2 and /Ey/2 on the x-y and x-z planes, respectively. The electric field intensity /E/2 was strongly squeezed within the 20-nm air gap; therefore, the optical resonance may have been sensitive to the perturbation due to this deep subwavelength air gap of width d. The eigenfrequency of the SPP cavity mode was 193.6 THz with a corresponding resonance wavelength of λr = 1548.71 nm. The mode volume and quality factor were Vm = 14 × 10−3λr3 and Q = 544, respectively. Fig. 3c,d show the variations of the /E/2 field at the center of the air gap along the x-direction and close to the middle of the defect along the y-direction, respectively. The /E/2 field distribution is symmetric with respect to the middle of the cavity along the x-direction and rapidly decays away from the air gap region.

f3: /E/2 and /Ey/2 field distributions of the SPP cavity mode on the (a) x-y and (b) x-z planes, respectively.The result is obtained using the supercell approach with seven lattice periods on each side of the cavity. The cavity mode is confined by the cavity and squeezed inside the air gap. Variations of the /E/2 field for the cavity mode (c) at the center of the air gap along the x-direction and (d) close to the middle of the defect along the y-direction, respectively. In (c) x/a = 0 denotes the cavity center, and in (d) y/d = 0 denotes the silver substrate surface.

Mentions:
We generated defects in the structure to serve as a nanocavity by removing two circular air holes at the middle of the silicon photonic crystal beam, as shown in Figs 1a and 3a. The nanocavity supported a highly confined SPP cavity mode by means of the simultaneous SPP and bandgap effects, which confine propagation along the z-direction and x-direction, respectively. Fig. 3a,b show clearly the confinement of the field distributions /E/2 and /Ey/2 on the x-y and x-z planes, respectively. The electric field intensity /E/2 was strongly squeezed within the 20-nm air gap; therefore, the optical resonance may have been sensitive to the perturbation due to this deep subwavelength air gap of width d. The eigenfrequency of the SPP cavity mode was 193.6 THz with a corresponding resonance wavelength of λr = 1548.71 nm. The mode volume and quality factor were Vm = 14 × 10−3λr3 and Q = 544, respectively. Fig. 3c,d show the variations of the /E/2 field at the center of the air gap along the x-direction and close to the middle of the defect along the y-direction, respectively. The /E/2 field distribution is symmetric with respect to the middle of the cavity along the x-direction and rapidly decays away from the air gap region.

Bottom Line:
The crystal nanocavity used in this study consisted of a defective photonic crystal beam coupled to a metal surface with a nanoscale air gap in between and provided hybridization of a highly confined plasmonic-photonic mode with a high quality factor and deep subwavelength mode volume.Efficient photon-phonon interaction occurs in the air gap through the SAW perturbation of the metal surface, strongly coupling the optical and acoustic frequencies.As a result, a large modulation bandwidth and optical resonance wavelength shift for the crystal nanocavity are demonstrated at telecommunication wavelengths.

ABSTRACTWe propose dynamic modulation of a hybrid plasmonic-photonic crystal nanocavity using monochromatic coherent acoustic phonons formed by ultrahigh-frequency surface acoustic waves (SAWs) to achieve strong optomechanical interaction. The crystal nanocavity used in this study consisted of a defective photonic crystal beam coupled to a metal surface with a nanoscale air gap in between and provided hybridization of a highly confined plasmonic-photonic mode with a high quality factor and deep subwavelength mode volume. Efficient photon-phonon interaction occurs in the air gap through the SAW perturbation of the metal surface, strongly coupling the optical and acoustic frequencies. As a result, a large modulation bandwidth and optical resonance wavelength shift for the crystal nanocavity are demonstrated at telecommunication wavelengths. The proposed SAW-based modulation within the hybrid plasmonic-photonic crystal nanocavities beyond the diffraction limit provides opportunities for various applications in enhanced sound-light interaction and fast coherent acoustic control of optomechanical devices.